code: def abs(expr):
      expr = ast.IdExpr(expr, to_reuse=True)
      return ast.IfExpr(
          utils.lt(expr, ast.NumVal(0.0)),
          utils.sub(ast.NumVal(0.0), expr),
          expr,
      )
  
file_path: m2cgen/m2cgen/assemblers/fallback_expressions.py
imports: import math
  from m2cgen import ast
  from m2cgen.assemblers import utils
label_desc: Use image node_id 1 for calling a global function with example usage: abs(expr) and returns: ast